Bicycle rear wheel sprocket arrangements are generally known. They are used in touring bicycle, racing bicycle, and mountain bike sectors where derailleur mechanism gears are provided in bicycles in order to bring about different transmission ratios from the pedal crank to the rear wheel. In this instance, the number of sprockets on the rear wheel has always increased over time in order to graduate transmission ratios more and more finely. This fineness of the graduation was even further supported by an increasing number of chain rings on the pedal crank.
Recently, there has been a development tendency which reduces the number of chain rings which are directly connected to the pedal crank. This may lead to the so-called one-fold derailleur mechanisms in which only a single chain ring is provided on the pedal crank. With the reduction in the number of chain rings, the number of sprockets in the rear wheel sprocket arrangement and the tooth number graduation thereof assumes increasing importance for producing desired transmission ratios.
Reference may be made to the publication U.S. Pat. No. 3,748,916 A of Morse by way of example of a bicycle rear wheel sprocket arrangement of the generic type for a one-fold derailleur mechanism. This publication discloses a bicycle rear wheel sprocket arrangement with a total of 5 sprockets, of which the smallest may have 9 and the largest may have 45 teeth. Consequently, that sprocket arrangement has a gear range quotient of 45:9=5. Consequently, the gear range quotient is a measurement for the bandwidth of transmission ratios which can be produced with a sprocket arrangement. The greater the value of the gear range quotient, the greater is the bandwidth of transmission ratios which can be produced.
The technically most advanced prior art in the field of one-fold derailleur mechanisms may currently be a system which is marketed by SRAM under the name “XX1”. This system with a rear wheel sprocket arrangement comprising 11 sprockets has a gear range quotient of 4.2.
Furthermore, the XX1 system comprises a rear derailleur. The derailleur is coordinated in its geometry to the cassette and ensures that the chain tension in all transmission ratios corresponds to the requirements. The geometry (angle and length) of the cage and the tensioning device are particularly of importance for this purpose and have to be adapted to the number and size of the sprockets.
The known derailleur of the XX1 system can furthermore be set by means of a set screw (B screw) so as to be pivotable about the joint head axis with respect to the bicycle frame. The derailleur can therefore be adapted to the size of the cassette. By means of the set screw, the derailleur pivots about the joint head axis in order to set a predefined distance between the upper or sprocket-closer shift roller and that tooth of the largest sprocket which is closest to the shift roller. In other words, a distance between the outside diameter of the upper shift roller and the outside diameter of the largest sprocket, which distance is specific to and is predetermined for the components of the drive arrangement, is set. Said distance, the free chain length between the upper shift roller and an active sprocket may also be mentioned, should always be approximately identical in size in order to maintain friction-free shifting. The drive arrangement is described in DE 10 2012 204 452 A1.
Shift systems are also known, the derailleur of which is pre-tensioned in relation to the frame by means of a spring in the joint head and in which the distance between shift roller and sprocket is adapted by changing the spring setting.
Specifically bicycle rear wheel sprocket arrangements with a high number of sprockets and/or a great difference in number of teeth between the largest and the smallest sprocket require a precise setting of the predefined distance. The greater the axial and/or radial extent of the rear sprocket arrangement, the greater is the path of movement of the derailleur. Reliable and friction-free shifting for the entire rear sprocket arrangement can be ensured only with a precise setting.
To date, the setting of the predefined distance has been possible only imprecisely by counting the free chain links (free chain length) between the upper shift roller and the active sprocket. This disadvantage of the defective and complicated setting of the drive arrangement is overcome by another aspect of the invention, a setting aid device or apparatus according to an embodiment and the simple use thereof.
Reference is further made as additional prior art to EP 2 022 712 A of Campagnolo, which discloses a 12-fold sprocket arrangement whose smallest sprocket has 11 teeth and whose largest sprocket has 27 teeth. The gear range quotient of that sprocket arrangement is, at 2.45, slightly less than half as large as that of the sprocket arrangement of the previously discussed U.S. patent.
Reference may be made to U.S. Pat. No. 5,954,604 A of Shimano as another extreme example of a multiple sprocket arrangement which sets out a sprocket arrangement having 14 sprockets. FIG. 13 of this publication shows an embodiment in which the smallest sprocket of the sprocket arrangement has 11 teeth and the largest sprocket has 39 teeth. Therefore, the gear range quotient of that known sprocket arrangement is 3.54.
In a more comprehensible manner, the number of sprockets in the sprocket arrangement gives a measurement of the fineness of the graduation of the transmission ratios which can be achieved with a rear wheel sprocket arrangement. The higher the number of sprockets, the finer the graduation of the adjustable transmission ratios can be.
However, there may be only limited structural space available for the arrangement of the rear wheel sprocket arrangement on a rear wheel hub so that the number of sprockets in the sprocket arrangement cannot be freely increased. Therefore, the packing density quotient mentioned in the introduction directly gives a measurement of how effectively the structural space present on the rear wheel hub is used for the arrangement of sprockets. Indirectly, the packing density quotient is also a measurement concerning the fineness of the graduation of the achievable transmission ratios because it contains in the numerator information concerning the number of sprockets in the rear wheel sprocket arrangement. Again, the following applies: the higher the packing density quotient, the more effective is the use of structural space for the arrangement of sprockets. The packing density quotient is, similar to the gear range quotient, a dimensionless numerical value, for the establishment of which only the numerical value of the spacing measured in millimetres between the axially outermost sprockets should be used.
The 5-fold sprocket arrangement known from U.S. Pat. No. 3,748,916 A takes up, for example, an axial structural space of approximately 26 millimetres. Consequently, the packing density quotient purely as a numerical value variable of this sprocket arrangement is 0.192.
In comparison, EP 2 022 712 A for the 12-fold sprocket in the most advantageous disclosed case, the implementation of which is not demonstrated in the publication, however, sets out an axial structural space requirement of 40.5 millimetres. This results in a packing density quotient of 0.296.
The above-mentioned 1-fold derailleur system XX1 of the same Applicant has, with 11 sprockets in a structural space of 38.4 millimetres, a packing density quotient of 0.286.
Finally, reference may be made as an additional comparison to the above-mentioned U.S. Pat. No. 5,954,604 A in which 14 sprockets of a sprocket arrangement are received with an axial spacing of the outermost sprockets which axially measures approximately 50 millimetres, which results in a packing density quotient of approximately 0.28.
Evidently, modern rear wheel sprocket arrangements have a packing density quotient of slightly below 0.3. This sets out the current state of axial structural space use on rear wheel hubs. The overview set out above of different existing rear wheel sprocket arrangements shows that either existing sprocket arrangements offer a large bandwidth of transmission ratios, but they are then graduated in a relatively coarse manner and distributed over a relatively large axial structural space, or existing sprocket arrangements offer a very fine graduation of relatively narrow bandwidths of transmission ratios, but then with very effective use of the axial structural space available.
The existing sprocket arrangements for bicycle rear wheels no longer comply in each case with the increasing demands placed on them. In view of the most recent technical trends in the development of bicycle components as described in the introduction, it is no longer sufficient to graduate bandwidth of transmission ratios only in a very coarse manner or to offer only a small bandwidth of transmission ratios. In particular, but not exclusively, in the case of a one-fold derailleur mechanism having only one chain ring, a large bandwidth of transmission ratios which is graduated in a relatively fine manner and which has space in conventional bicycle constructions is required on the rear wheel. For this purpose, a new class of bicycle rear wheel sprocket arrangements is required.
Given this background, it is the object of the present disclosure to provide a drivetrain or drive arrangement for a bicycle as is described herein.